Wednesday, September 27, 2017

Migrating a Model to Keras 2.0

Keras v2.0 has been released for a couple of months now - v2.0.0 released on 5th May, 2017, while the latest version is 2.0.8 at the time of this writing. It brought in a lot of new features and improvements, but also made some syntax changes. Trying to run a code with the old syntax may result in anything from a flood of deprecation warnings, to not being able to run the code at all. Since there are many code examples online which uses the older syntax - including some older posts in Codes of Interest - it's better to know how to get such older syntax model to work on the 2.0 API.

The complete list of changes in Keras v2.0 was extensive, but the following list would help you to narrow down majority of the changes.

The most prominent change is the changing of image_dim_ordering parameter to image_data_format, and its associated values from "tf", and "th" to "channels_last" and "channels_first". We talked about this change in detail in our earlier post "What is the image_data_format parameter in Keras, and why is it important".

Likewise, in all the places where "dim_ordering" argument/parameter was used, it has been changed to "data_format".

All of the Convolution* layers have now need renamed to Conv*.
E.g. Convolution2D is renamed to Conv2D

Saturday, September 9, 2017

What is the image_data_format parameter in Keras, and why is it important

We've talked about the image_dim_ordering parameter in Keras and why is it important. But since from Keras v2 changed the name of the parameter, I thought of bringing this up again.

As you know, Keras  is a higher-level neural networks library for Python, which is capable of running on top of TensorFlow, CNTK (Microsoft Cognitive Toolkit), or Theano, (and with limited support for MXNet and Deeplearning4j), which Keras refers to as 'Backends'.

Which backend Keras should use is defined in the keras.json file, which is located at ~/.keras/keras.json in Linux and Mac OS, and at %USERPROFILE%\.keras\keras.json on Windows.

The default keras.json file (default set to TensorFlow) would look like this,
 {  
   "epsilon": 1e-07,  
   "floatx": "float32",  
   "image_data_format": "channels_last",  
   "backend": "tensorflow"  
 }  
The "backend" parameter should either be "tensorflow", "cntk", or "theano". When switching the backend, make sure to switch the "image_data_format" parameter too. For "tensorflow "or "cntk" backends, it should be “channels_last”. For “theano”, it should be “channels_first”.